Conventional office chairs frequently include a seat-back arrangement which is connected to a base by a tilt mechanism. The tilt mechanism defines one or more pivot axes about which a seat or back assembly may pivot or tilt relative to the base. Office chairs typically tilt rearwardly about fixed horizontal pivot axes wherein the seat and back assemblies are rearwardly tiltable either together or independently. To resist such tilting and bias the seat and back assemblies to normal upright positions, numerous tilt mechanisms have been provided which include springs such as coil, leaf and torsion springs which oppose the tilting movement.
As an alternative to conventional spring arrangements, prior tilt control mechanisms have also used elastomeric pads or rings between relatively moving surfaces. The pads or rings are resilient so as to be compressed between the moving surfaces to resist the tilting movement. Some of these tilt mechanisms permit the seat to pivot in multiple directions.
Examples of chairs using elastomeric pads or rings which permit tilting in multiple directions are disclosed in U.S. Pat. Nos. 139,948, 3,309,137, 4,027,843, and 5,573,304. The U.S. Pat. No. 3,309,137 patent permits adjustment of tilting resistance by varying the compression of an elastomeric ring. The chairs disclosed in the remaining patents do not permit adjustment of the tilting resistance.
In another chair as disclosed in U.S. Pat. No. 4,890,886, the tilt control mechanism defines a fixed pivot axis between the seat assembly and the chair base. The tilt control mechanism further includes a plate secured to the seat assembly so as to move with the seat assembly relative to the base, and a second plate which is spaced apart from the first plate and remains stationary relative to the base. These opposing plates move relative to each other during tilting of the seat assembly, and elastomeric pads are provided between these relatively movable plates to resist tilting and bias the seat assembly to a neutral position. These pads have predetermined and fixed size and shape and therefore, the elastic characteristics of these pads are predefined and constant. To adjust resistance to tilting, the elastomeric pads are movable relative to the pivot axis to thereby adjust the distance defined therebetween. In one embodiment, the pads are vertically movable.
However, users, such as office workers, who sit in such chairs typically move in all directions, such as sidewardly, forwardly and rearwardly when working. Conventional tilt control mechanisms having fixed axes, however, restrict such movement due to the fixed axes, and hence do not readily accommodate the usual movements of a user such as movement to the side.
To more readily accommodate the various movements of a user, the chair of the present invention accommodates movement of a user both forwardly and sidewardly and in fact permits the chair seat to swivel about a connection point so as to react to the user. In particular, to overcome the disadvantages of conventional chair designs which use fixed pivot axes, the chair of the present invention includes a tilt control mechanism which permits universal tilting or swiveling of the seat assembly relative to the base in substantially all horizontal directions. The seat assembly is not restrained by fixed pivot axes but instead effectively pivots about a pivot or connection point. Thus, the seat assembly can pivot forwardly and rearwardly, sidewardly and in any other horizontal direction extending radially away from the pivot point, and can also be swivelled about the connection point. Thus, as a user shifts and moves, the chair reacts to the user's movements while still providing sufficient resistance to the universal tilting movement to provide stability and control for the user.
To provide resistance to such tilting, the tilt control mechanism of the invention includes a vertical support column which is supported on the base and remains stationary. To resist tilting, the support column includes an elastomeric doughnut-shaped ring which is fixed in position on an upper end of the column proximate the pivot connection. The resilient ring has predefined vertical and radial dimensions.
In an embodiment of the invention, the tilt control mechanism includes a cylindrical housing which is disposed in concentric and surrounding relationship to the support column and the resilient ring supported thereon. The housing is movable with the seat assembly during tilting thereof wherein the resilient ring resists movement of the housing relative to the support column.
The resilient ring applies a reaction force on the housing as the housing moves relative to the support column and therefore, biases the housing to return the seat assembly to a normal or neutral position. The resilient ring, however, does not directly contact the housing but instead, an annular sleeve is slidably received in a space defined between the resilient ring and the housing. The adjustment sleeve is close-fittingly received between the resilient ring and the housing such that the resistance force of the resilient ring is transferred to the housing.
The adjustment sleeve furthermore is movable to adjust the resistance to tilting. More particularly, the amount of surface contact between the sleeve and the resilient ring defines the extent of the resilient ring which effectively acts on the housing. Thus, while the resilient ring has a contact surface which has a fixed dimension, only a portion of this contact surface typically acts on the housing depending upon the amount of contact area between the sleeve and the resilient ring or in other words, the amount of the sleeve which is inserted between the resilient ring and the housing.
By varying the amount of surface contact, i.e. the contact area, between the resilient ring and the adjustment sleeve, the effective size of the resilient ring is continuously variable whereby the effective spring characteristic of the resilient ring as it acts on the housing is continuously adjustable. This arrangement, thereby, adjusts tilting resistance by varying the effective spring characteristics of the resilient ring. While the sleeve preferably moves vertically, alternate embodiments are also disclosed herein wherein the sleeve is moved horizontally to vary the contact area between the sleeve and the resilient ring and adjust tilting resistance.